The present invention relates to a monolithic electroluminescent device of a semiconductor body on which extends a semiconductor region forming a junction with the said body and having electroluminescent properties when minority charge carriers are injected in it, the said body and the said semiconductor layer being provided with electrodes permitting of connecting them to a source of electric energy.
Although the expression light applies in the usual manner to a radiation situated in the visible spectrum, it is to be noted that the luminescence and the light emission considered here relate to the emission of photons of any energy situated or not situated in the visible spectrum.
It is known that the luminescence in electroluminescent diodes is produced by certain recombinations of charge carriers when, for example, minority charge carriers are injected into an adequate semiconductor material by means of a p-n junction polarized in the forward direction. It appears desirable not only to improve the efficiency of said electroluminescent diodes but also to be able to localize and locally control the light emission by simple means which are compatible with the dimensions, the materials and the electric quantities which are of the domain of micro-electronics.
The localisation of the emission permits of considering, for example, monolithic display structures of which the motive to be visualized is obtained by selective excitations of electroluminescent elements.
The efforts to improve the luminous efficiency have up till now mainly related to the reduction of losses by absorption and reflection and to the choice of a material having a high internal luminous efficiency; the control or modulation devices of the light emission have so far been devices for controlling current traversing the diodes for which reason they are comparatively important and necessitate connections of a large sectional area, auxiliary means of high power.
The localisation of the light emission, notably in the materials having an indirect band structure which are transparent to their own radiations, must be obtained by means of opaque zones dividing, for example, a region of an electroluminescent diode in optically distinct elements which are controlled individually by current. Said zones often occupy a considerable surface area.
In French Pat. No. 1,538,071, means are proposed to influence the part of the junctions where the light emission must be eliminated. However, said means only influence the junction and the immediately adjacent zone and they cannot influence the whole luminescent surface of a localized region. Moreover, the lateral electrodes required in said devices to create the necessary electric fields occupy a considerable surface area beside luminescent regions, which diminishes to the same extent the surface area available for the latter.
Structures comprising a dielectric layer and a metal grid applied to a semiconductor diode having already been used to influence the rate of recombination of minority carriers, for example, the structure of the semiconductor device described in the U.S. Pat. No. 3,102,201. In these devices, however, the electric field permitting modulating the light emission covers the whole extent of the junction and uniformly influences in depth the whole extent; the modulation obtained is a modulation in time and said devices do not comprise the possibility of localizing the light emission.
It is mainly the object of the invention to mitigate said drawbacks and said insufficiencies and the invention proposes inter alia to provide an monolithic electroluminescent device comprising a simple means by which the light efficiency and the control and the localisation of the light emission can easily be improved.